1. Field of the Invention
The present invention relates generally to a transmission line pressure control system which includes a self-adjust function wherein the line pressure level is adjusted during the operation of the transmission in a manner which compensates for unit to unit differences and wear which occurs with the passing of time, and more specifically to such a system which inhibits the self adjust function in the event that pertinent sensors malfunction.
2. Description of the Prior Art
An automatic transmission Service Manual (publication A261C07) issued in March 1987 relating to the so called RE4RO1A type transmission describes an arrangement which utilizes tabled data for controlling the line pressure during shifting and non-shifting modes of transmission operation. In this arrangement the engine throttle valve opening degree is used to determine the duty cycle of a signal used to control a line pressure control solenoid valve.
However, the solenoids used for the purposes of line pressure control and the friction elements used in a given transmission, inevitably exhibit a unit to unit variation and/or exhibit a change in characteristics with the passing of time due to wear and the like deterioration.
Accordingly, the transmission control tends to deteriorate to the point of permitting strong shift shocks and/or excessive friction element slippage which shortens the working life of the friction elements per se.
The above mentioned changes and/or unit to unit variations cannot be compensated unless it is possible to change the line pressure control valve duty cycle.